1. Field of the Invention
This invention relates to an objective lens-driving apparatus that controllably corrects errors in tracking grooves or pits formed in an optical recording medium such as an optical disk. The invention also relates to an objective lens-driving apparatus that controllably corrects errors in focusing a beam of light on an optical recording medium such as an optical disk.
2. Description of the Related Art
When signals are recorded onto or reproduced from an optical recording medium through an objective lens, a control is required to position the objective lens in such a way that a light spot is always focussed on the recording grooves or pits accurately. Many of such objective lens-driving apparatuses are of a moving coil type.
However, the moving coil type requires a means for supplying electric power from a stationary part of the apparatus to a coil on a movable part. This power supplying means adversely affects the drive characteristic of the objective lens-driving apparatus, preventing the objective lens from being highly accurately positioned. In addition, the coil requires to be electrically connected to the power supplying means but this electrical connection is rather difficult.
In order to solve these problems, for example, Japanese Patent Hei No. 7-19388 proposes a moving magnet type objective lens driving apparatus.
FIG. 25 is a perspective view, with a partially cutaway view, of a pertinent portion of the conventional apparatus disclosed in Japanese Patent Hei No. 7-19388.
Referring to FIG. 25, flat focusing coils 124a and 124b and flat tracking coils 125a and 125b are wound generally in a flat plane, and securely supported by walls 103a and 103b in opposing vertical planes. The walls 103a and 103b are in one-piece construction with a base 101. A lens holder 110 is rotatably supported on a shaft 109 securely fixed to the base 101, and supports an objective lens 113 and magnets 116a and 116b thereon.
A supporting spring 118 is in the shape of a square loop and maintains the lens holder 110 at its neutral position. A pair of opposing sides of the spring 118 is fixed to the lens holder 110 and another pair of opposing sides engages retaining plates 107 and 107b (only 107b is depicted) to be fixed to the base 101.
When a focus error is corrected, a predetermined electric current is run through the focusing coils 124a and 124b to create an electromagnetic force acting between the current and the magnetic field emanating from the magnets 116a and 116b for focusing control. This electromagnetic force drives the lens holder 110 in a direction perpendicular to the surface of the optical recording medium.
When a tracking error is corrected, a predetermined electric current is run through the tracking coils 125a and 125b so that the lens holder 110 is driven in a direction transverse to the track in the optical recording medium for tracking control.
The aforementioned conventional objective lens driving apparatus requires the spring 118 that supports the lens holder rotatably and holds the objective lens at its neutral position. The use of the spring 118 increases the number of components and makes the assembly operation of the apparatus complex.
A magnetic circuit is formed of only the magnets 116a and 116b and therefore the magnetic field generated by the magnetic circuit is rather weak. As a result, this conventional apparatus makes drive sensitivity low and requires more electric power accordingly.
A small gap between the support shaft 109 and lens holder 110 can cause rattling of the lens holder 110 and/or tilting and vibration of the objective lens 113.
An object of the present invention is to solve the aforementioned problems.
An object of the invention is to provide an objective lens driving apparatus that requires no specific component to keep the objective lens at its neutral position and facilitates assembly operation of the apparatus.
Another object of the invention is to provide an objective lens driving apparatus where mechanical vibration due to the gaps between bearings is minimized during operation.
A still another object is to provide an objective lens driving apparatus where drive sensitivity of a lens holder is increased, thereby implementing a low-power consumption operation.
An objective lens driving apparatus is used for positioning an objective lens accurately to form a light spot on grooves or pits on an optical recording medium. An objective lens has an optical axis and focusing light emitted from a light source on an information-recording medium. A lens holder holds the objective lens and having a bearing hole that extends in a direction parallel to the optical axis. A shaft is inserted into the bearing hole so that the lens holder is rotatably supported on the shaft. A pair of magnets supported on the lens holder, the magnets being diametrically opposite to one another with respect to the shaft. A base is made of a magnetic material and has a pair of coil-supporting yokes. The pair of coil-supporting yokes are disposed such that each of the pair of magnets exerts an attraction force on a corresponding one of the pair of portions to urge the lens holder both in a direction of the optical axis and in a direction perpendicular to the optical axis. A first set of first focusing coil and tracking coil and a second set of focusing coil and tracking coil are mounted to the pair of portions of the base. The first and second sets are diametrically opposite with respect to the shaft in such a way that the pair of magnets are between the first and second sets.
The objective lens driving apparatus further includes the focusing coil of each of the first and second sets has a first axis of coil, and the tracking coil of each of the first and second sets has a second axis of coil substantially perpendicular to the first axis of coil. When a first current flows through the focusing coil of each of the first set and second set, an urging force in a direction parallel to the shaft is generated between a corresponding magnet and the focusing coil. When a current flows through the tracking coil of each of the first set and second set, an urging force in a direction substantially perpendicular to the shaft is generated between a corresponding magnet and the tracking coil.
An objective lens driving apparatus is used for positioning an objective lens accurately to form a light spot on grooves or pits on an optical recording medium. An objective lens has an optical axis and focuses light emitted from a light source on an information recording medium. A lens holder holds the objective lens and has a bearing hole that extends in a direction parallel to the optical axis. A shaft is inserted into the bearing hole so that the lens holder is rotatably supported on the shaft. A pair of magnets are supported on the lens holder and diametrically opposite to one another with respect to the shaft. A pair of coil-supporting yokes are made of a magnetic material. A base is made of a non-magnetic material and holds the pair of coil supporting yokes. The coil supporting yokes are disposed such that each of the pair of magnets exerts an attraction force on a corresponding one of the pair of portions to urge the lens holder both in a direction of the optical axis and in a direction perpendicular to the optical axis. A first set of first focusing coil and tracking coil and a second set of focusing coil and tracking coil are mounted to the pair of portions of the base. The first and second sets are diametrically opposite with respect to the shaft in such a way that the pair of magnets are between the first and second sets.
An objective lens driving apparatus is used for positioning an objective lens accurately to form a light spot on grooves or pits on an optical recording medium. An objective lens has an optical axis and focusing light emitted from a light source on an information-recording medium. A lens holder holds the objective lens and has a bearing hole (6a) that extends in a direction parallel to the optical axis. Two magnets are supported on the lens holder and are diametrically opposite to one another with respect to the shaft. A shaft is inserted into the bearing hole so that the lens holder is rotatably supported on the shaft. Two coil-supporting yokes are made of a magnetic material. Two yoke carrying members are made of a non-magnetic material. Each of the pair of supporting yokes holds a corresponding one of the pair of coil supporting yokes. A base is made of a non-magnetic material and has the shaft. The base has a pair of magnetic portions disposed such that each of the two magnets exerts an attraction force on a corresponding one of the pair of magnetic portions. Thus, the lens holder is urged both in a direction of the optical axis and in a direction perpendicular to the optical axis. A first set of first focusing coil and tracking coil and a second set of focusing coil and tracking coil are mounted to the pair of portions of the base.
The first and second sets are diametrically opposite with respect to the shaft in such a way that the pair of magnets are between the first and second sets.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.